The prior art is extensive. Many seals have been developed which, at least when newly installed, will provide excellent sealing. Prior forms include seals with tapered cross sectional shapes combined with tapered metal followers in gland nut assemblies, such as those disclosed in U.S. Pat. No. 2,021,745 issued to Pfefferle et al. In practice it has been found that the useful life of such seals is limited especially when high and variable temperatures are encountered. All-metal sealing assemblies employing tapered rings, followers and the like are well known, the U.S. Pat. No. 3,380,765 to Himmel showing several such concepts. Further, the concept of line contact between the tapered parts is also recognized as not being shown, for example, in U.S. Pat. No. 3,265,413 issued to Currie wherein the line contact is stated as being capable of being "widened with moderate clamping pressure" indicating that the resiliency of metal parts, although limited, is useful in sealing techniques. Other prior art of which applicants are aware includes the following fairly recently issued patents:
U.S. Pat. No. 3,171,935 to Gloeckler; PA1 U.S. Patent No. 3,186,743 to Russell; PA1 U.S. Pat. No. 3,694,010 to Callahan; and PA1 U.S. Pat. No. 2,951,721 to Asp.
The last above mentioned patent includes a detailed discussion of the use of seals constructed of TEFLON in several forms.
There is a need, however for a seal which will last almost indefinitely when the the use thereof is not persistent and which will have a useful life of years even when the use is continuous or under conditions of varying temperatures.